1. Field
The following description relates generally to a system for converting thermal energy into electric energy, and in particular, a system for utilizing the thermoacoustic effect to convert a thermal gradient into electric energy.
2. Background
Hydrothermal vents are common natural phenomena where geothermally heated water emanates from the earth. Some types of hydrothermal vents are located on the sea floor, frequently at mid-ocean ridges at the boundaries between tectonic plates. FIG. 1 is a simplified illustration showing a certain type of hydrothermal vent. Here, ambient sea water 2 is drawn into the sea floor 4. Due to subsurface magma, at depths the sea floor includes heated layers 6, wherein the seawater drawn into the sea floor is heated to high temperatures and expelled through a hydrothermal vent 8 back into the ocean. In some hydrothermal vents, due to a buildup of minerals that the seawater picked up while being drawn through the sea floor, a chimney 10 may occur.
Due to this natural phenomenon, a large, naturally occurring temperature gradient is created where superheated hydrothermal fluid 12 issues into cold sea water. For this reason, there has been interest in harvesting energy from undersea hydrothermal vents. However, a number of practical difficulties have prevented any large-scale generation of energy at undersea hydrothermal vents. For example, the vents are highly inaccessible, typically occurring at remote locations under thousands of meters of water. Further, when expelled from the vents, the hydrothermal fluid generally contains a concentration of minerals and various compounds and is frequently acidic and corrosive, potentially destroying most types of conventional electric generating equipment in short order. Moreover, even the primary feature that makes these vents desirable, that is, the extreme thermal gradient between the hydrothermal fluid and the surrounding sea water (e.g., a temperature change from about 350° C. to 2° C. in a distance of just a few feet) is so great as to make the use of conventional heat pumps, stirling engines, or steam turbines difficult or impossible. In addition, these devices each have many moving parts and other issues that reduce their reliability, resulting in the need for relatively frequent maintenance, which is much more difficult to perform at the deepwater locations where the hydrothermal vents occur.